The overall objectives of this project continue to be related to differentiative pathways of lymphoid cells in humans. Emphasis is on B-\and T-cell differentiation and bone marrow differentiation. Differentiation is studied in both normal and malignant cell populations, e.g., in leukemia and lymphoma. The significance of these studies relates primarily to improved understanding of the immune system and its normal function, as well as the abnormal function in immunodeficiencies, autoimmune disorders, and especially, in leukemias and lymphomas. (MI)